Unfogged,primitive,silver halide emulsions containing desensitizing amounts of optical sensitizing dyes and the use thereof in reversal processes

ABSTRACT

IMPROVED PROCESSES ARE DISCLOSED FOR OBTAINING POSITIVE IMAGES IN AN UNFOGGED, PRIMITIVE, SILVER HALIDE EMULSION WHEREIN A PHOTOGRAPHIC ELEMENT COMPRISING A SUPPORT AND SAID EMULSION ARE IMAGEWISE-EXPOSED AND THEN EITHER (1) DEVELOPED IN A SILVER HALIDE DEVELOPER IN THE PRESENCE OF A SILVER HALIDE FOGGING AGENT OR (2) GIVEN A HIGHINTENSITY LIGHT FLASH BEFORE DEVELOPMENT IN A SILVER HALIDE DEVELOPER. IN ONE ASPECT, THE SILVER HALIDE EMULSIONS OF THIS INVENTION ARE UNFOGGED, PRIMITIVE, SILVER HALIDE EMULSIONS WHICH CONTAIN A DESENSITIZING CONCENTRATION OF A SPECTRAL-SENSITIZING DYE. IN ONE PREFERRED EMBODIMENT, THE PRIMITIVE SILVER HALIDE EMULSION CONTAINING A DESENSITIZING LEVEL OF A DESENSITIZING DYE IS (1) IMAGEWISE-EXPOSED, (2) GIVEN AN OVER-ALL FLASH EXPOSURE WITH A RELATIVELY SHORTDURATION, HIGH-INTENSITY LIGHT AND (3) DEVELOPED IN A SILVER HALIDE DEVELOPER.

United States Patent '0 UNFOGGED, PRIMITIVE, SILVER HALIDE EMUL- SION S CONTAINING DESENSITIZING AMOUNTS F OPTICAL SENSITIZING DYES AND THE USE THEREOF IN REVERSAL PROCESES Susan Starr Collier, Le Roy, and Paul Brewster Gilmau, Jr., Rochester, N.Y., Henry Linschitz, Waltham, Mass, and Ronald George Raleigh, Brockport, N.Y., assignors to Eastman Kodak Company, Rochester, N.Y. N0 Drawing. Filed June 17, 1971, Ser. No. 154,154

Int. Cl. G03c /24 US. Cl. 9664 13 Claims ABSTRACT OF THE DISCLOSURE Improved processes are disclosed for obtaining positive images in an unfogged, primitive, silver halide emulsion wherein a photographic element comprising a support and said emulsion are imagewise-exposed and then either (1) developed in a silver halide developer in the presence of a silver halide fogging agent or (2) given a highintensity light flash before development in a silver halide developer. In one aspect, the silver halide emulsions of this invention are unfogged, primitive, silver halide emulsions which contain a desensitizing concentration of a spectral-sensitizing dye. In one preferred embodiment, the primitive silver halide emulsion containing a desensitizing level of a desensitizing dye is (1) imagewise-exposed, (2) given an over-all flash exposure with a relatively shortduration, high-intensity light and (3) developed in a silver halide developer.

This invention relates to silver halide emulsions a d methods of forming positive images in silver halide emulsions. In one aspect, this invention relates to a system for forming positive images which utilizes a photographic element having at least one layer containing an unfogged, primitive, silver halide composition and a desensitizing concentration of a spectral-sensitizing dye having a cathodic halfwave potential less positive than --1.0. In another aspect, this invention relates to an improved method of obtaining positive images wherein an unfogged, primitive, silver halide composition which contains a desensitizing amount of a spectral-sensitizing dye having a cathodic halfwave potential less positive than l.0 is imageWise-exposed with a low-intensity exposure and then either (1) is given a light flash before development in a silver halide developing composition or (2) is developed in the presence of a silver halide fogging agent to produce the positive image.

. Processes are known in the art for making positive images in unfogged silver halide emulsions by imagewise exposure followed by fogging developers, etc. Typical processes of this type are disclosed in US. Pats. 2,497,875 by Falleson issued Feb. 21, 1950; 2,588,982 by Ives issued Mar. 11, 1952; and 2,456,953 by Knott et al. issued Dec. 21, 1948; British Pat. 1,151,363; and Japanese Pat. 2 9405/68 issued Dec. 17, 1968. Generally, the prior processes used internal-image silver halide emulsions such as emulsions made by the conversion technique of Davey et al. US. Pat. 2,592,250, emulsions made by the techniques disclosed in British Pat. 1,011,062, and the like. The emulsion could be used to make positive images by 3,736,140 Patented May 29, 1973 the above techniques, but improved photographic characteristics such as higher photographic speed, lower D higher D and the like are desired to obtain acceptance of this system in many applications of photography.

We have now found that unfogged, primitive silver halide emulsions which contain a desensitizing amount of a spectral-sensitizing dye having a cathodic halfwave potential less positive than -1.0 can be imagewise-exposed and then either given a flash exposure before development in a silver halide developer or developed in a silver halide developer in the presence of a fogging agent to produce a positive image. We have also found that increased efficiency of light absorption is obtained with the high-concentration levels of these dyes since one is not limited by concentrations which severely affect blue-speed desensitization which occurs when high concentrations of these dyes are used in surface-sensitive emulsions to form a negative image. Moreover, photographic elements of the present invention which are imagewise-exposed followed by a high-intensity flash exposure and development exhibit substantially reduced low-intensity reciprocity failure compared to an identical element which is imagewise-exposed and processed to form a negative image.

In a highly preferred embodiment, photographic elements containing the emulsions of this invention are imagewise-exposed with a low-intensity light, given an over-all flash with a high-intensity light and then developed in a silver halide developer to provide a positive image. The imagewise exposure is given with a lowintensity light at .01 and preferably .05 second or longer and the over-all high-intensity flash is of a duration of less than 0.05 and preferably less than 0.01 second with optimum flash intensity and duration depending on the specific intensity used in the exposure step.

In another preferred embodiment, the primitive silver halide emulsions are substantially free of any sulfur or nobel-metal sensitization, either internally or on the sur face of the silver halide grain.

In another preferred embodiment, the emulsions of this invention are imagewise-exposed and then processed in a silver halide developing composition in the presence of a hydrazine fogging agent.

In another preferred embodiment, the emulsions of this invention are imagewise-exposed and then processed in a silver halide developer composition in the presence of a reactive N-substituted cycloammonium quaternary salt.

In still another'embodiment where emulsions of this invention contain a spectral-sensitizing dye having a negative charge under conditions of development are to be developed in a developing composition in the presence of a fogging agent, a compound that decreases the negative charge density at the silver halidehalide surface and may make it positive is preferably incorporated in the emulsion or the developer, such as a quaternary compounds, a positively charged dye, and the like.

Generally, the emulsions of this invention are those emulsions which can be made by a simple silver halide precipitation in the absence of chemical or physical sensitizing conditions. Generally, the emulsions can be described as primitive silver halide emulsions which are substantally free of any specific chemically induced sensitivity internally, as well as on the surface of the grains. Preferably, the emulsions are those which are primitive emulsions, i.e., those derived from precipitation of an alkali metal halide and a Water-soluble silver salt in the presence of a peptizer and are substantially free of any additional sulfur and noble-metal sensitization.

The silver halides of this invention are un-fogged. Such emulsions contain only minimal developable surface latent images wherein processing for minutes at 27 C. in Kodak Developer DK-50 will produce a density of less than 0.3 and preferably less than 0.2.

In accordance with this invention, a simple exposure and development process can be used to form a positive image. The photographic element comprising at least one layer of a silver halide composition as described above can be (1) imagewise-exposed and then developed in a silver halide developer in the presence of a fogging agent or (2) imagewise-exposed with low-intensity light, given a flash over-all high-intensity exposure and then developed in a silver halide developer to provide a positive image record.

The imagewise exposure can be made by any conventional technique, daylight exposure and the like. Generally, an improved response is obtained at low intensity compared with the converted-type emulsions of the prior art. In those embodiments where the photographic elements are imagewise-exposed, given an over-all flash and then developed, the imagewise exposure is generally a low-intensity exposure of at least 0.01 second and, in highly preferred embodiments, at least seconds in duration, and the flash exposure is a high-intensity exposure of less than 0.05 second and preferably less than 10* sec onds wherein said flash has at least ten times the intensity of the imagewise exposure. Typical useful intensities for the imagewise exposure are generally in the range of about 5X10" to about 5 10 watts/ cm. However, lower intensities in the magnitude of 1 10- watts/cm. can be used for the imagewise exposure, such as those encountered in photographic systems used in astronomy. When extremely low-intensity exposures are used, the intensity of the over-all flash exposure is generally at least 5 10- watts/cm. or greater.

In those embodiments where the photographic elements are imagewise-exposed and then developed in the presence of a fogging agent, good reversal images are generally obtained when the sensitizing dye has a net positive charge. Where dyes having a neutral charge or a negative charge are used in desensitizing concentrations in the emulsion, a compound that decreases a negative charge at the silver halidehalide surface of the grain and may make it positive is incorporated in the emulsion or the developer. Suitable compounds include positively charged dyes, quaternary salts such as 1-phenylethyl-2-picolinium bromide, dodecyl trimethylammonium para-toluenesulfonate, and the like.

The developing compositions which can be used in the processes of the present invention can be either totalimage developing compositions which contain silver halide solvents or surface-image developing compositions. In certain preferred embodiments, however, the developing compositions utilized are surface developers.

It is understood that the term surface developer encompasses those developers which Will reveal the surface latent image on a silver halide grain, but will not reveal substantial internal latent image in an internal imageforming emulsion, and conditions generally used develop a surface-sensitive silver halide emulsion. The surface developers can generally utilize any of the silver halide developing agents or reducing agents, but the developing bath or composition is generally substantially free of a silver halide solvent (such as water-soluble thiocyanates, water-soluble thioethers, thiosulifates, ammonia and the like) which will crack or dissolve the grain to reveal substantial internal image. Low amounts of excess halide are sometimes desirable in the developer or incorporated in the emulsion as halide-releasing compounds, but high amounts are generally avoided to prevent substantial cracking of the grain, especially with respect to iodidereleasing compounds.

Typical silver halide developing agents which can be used in the developing compositions of this invention include hydroquinones, catechols, aminophenols, 3-pyrazolidones, ascorbic acid and its derivatives, reductones, phenylenediamines and the like or combinations thereof. The developing agents can be incorporated in the photographic elements wherein they are brought in contact with the silver halide after imagewise exposure; however, in certain embodiments they are preferably employed in the developing bath.

The sensitizing dyes utilized in the emulsions of this invention generally include all dyes known to be useful in spectrally sensitizing, silver halide emulsions, and preferably are those characterized as methine or polymethine dyes. According to the present invention, the respective dyes are used in concentrations of a greater amount than that necessary for obtaining an optimum sensitizing effect with an emulsion which has been only surfacesensitized. In one preferred embodiment, the sensitizing dyes are used in concentrations which generally desensitize a surface-sensitive emulsion. In this embodiment, the sensitizing dyes are used at a concentration above that which will lower the blue-speed sensitivity of a sulfurand gold-surface-sensitized, silver bromoiodide (6 mole percent iodide) emulsion of equivalent grain size at least 0.3 log E when developed in a surface developer such as Kodak D-19.

In another embodiment, the dyes are used at concentrations of above about 400 mg. per silver mole, especially when the silver halide emulsion has an average grain size of about 0.2 micron.

The dyes used in the emulsion combinations of this invention are characterized as being spectral-sensitizing dyes for silver halide emulsions including the ultraviolet, visible and infrared regions of the spectrum. The dyes are (further characterized as having a reduction potential or cathodic halfwave potential less positive than 1.0, i.e., such as cathodic halfwave potentials of -1.5, 2.0, etc. In certain embodiments, the useful dyes also have an anodic halfwave potential more positive than +0.4 and preferably more positive than H0.55.

Typical useful classes of dyes which can be used according to this invention include the methine dyes such as the cyanines, isocyanines, pseudocyanines, hemicyanines, merocyanines, oxanols, azacyanines and the like. Generally, any dye which can be used to sensitize spectrally a silver halide emulsion at low concentrations can now be used in high concentrations when used in the reversal systems according to this invention.

The halfwave potentials can be measured as disclosed in Illingsworth, U.S. Pat. 3,501,307 issued Mar. 17, 1970; for example, the cathodic measurements can be made with a 1 10- molar solution of the sensitizing dye in a solvent, such as methanol which is 0.05 molar in lithium chloride using a dropping mercury electrode with the polarographic halfwave potential for the most positive cathodic wave being designated E Anodic measurements can be made with 1X10 molar aqueous solvent solution, for example, methanolic solutions of the electron acceptor which are 0.05 molar in sodium acetate and 0.005 molar in acetic acid using a carbon paste of pyrolytic graphite electrode, with the voltammetric half peak potentials for the most negative anodic response being designated E,,. In each measurement in this application the reference electrode was an aqueous silver-silver chloride (saturated p0- tassium chloride) electrode at 20 C., but equivalent electrodes thereof could be used. Electrochemical measurements of this type are known in the art and are described in New Instrumental Methods in Electrochemistry, by Delahay, Interscience Publishers, New York, N.Y., 1954; Polarography, by Kolthoff and Lingane, 2nd Edition, In-

terscience Publishers, New York, N.Y., 1952; Analytical Chemistry, 36, 2426 (1964), by Elving; and Analytical Chemistry, 30, 1576 (1958), by Adams. Plus and minus signs are according to IUPAC (International Union of Pure and Applied Chemistry) Stockholm Convention 1953.

The silver halide emulsions of this invention can be developed in a silver halide developer in the presence of a fogging agent to provide good positive images. The fogging agent can be incorportaed in at least one layer of the silver halide element, which layer is in water-permeable association with the silver halide emulsion, or it can be contacted with said silver halide emulsion by a separate bath or simultaneously with the developer composition by incorporating the fogging agent into the developer composition. Generally, the useful fogging agents of this invention are those which provide nucleation or fog specks which initiate development of the silver halide in the unexposed areas before initiating substantial development in the exposed areas of an internal-image emulsion in a surface developer. Compounds of this type are generally not practical developing agents by themselves for silver halides and are referred to as selective fogging agents; in some documents they have been referred to generally as silver halide fogging agents or nucleating agents. Typical useful selective fogging agents include hydrazine compounds, reactive N-substituted cycloammonium salts and the like.

In one preferred embodiment of the invention, hydrazines are used as the fogging agent, such as the compounds disclosed in U.S. Pats. 2,588,982 by Ives issued Mar. 11, 1952, and 3,227,552 by Whitmore issued Jan, 4, 1966.

In another preferred embodiment, the fogging agents are reactive N-substitu-ted cycloammonium quaternary salts. Typical useful fogging agents of this type are disclosed in U.S. Ser. Nos. 28,041 by Lincoln et a1. filed Apr. 3, 1970, 85,706 by Kurtz et al. filed Oct. 30, 1970, and 85,709 by Kurtz et al. filed Oct. 30, 1970, which are incorporated herein by reference. Generally, these compounds can be represented by the formula:

wherein:

(A) Z represents the atoms necessary to complete a heterocyclic nucleus containing a heterocyclic ring of to 6 atoms including the quaternary nitrogen atom, with the additional atoms of said heterocyclic ring being selected from carbon, nitrogen, oxygen, sulfur and selenium;

(B) jrepresents a positive integer of from 1 to 2;

(C) a represents a positive integer of from 2 to 6;

(D) X represents an acid anion;

(E) R represents a member selected from:

(1) a formyl radical, (2) a radical having the formula:

wherein each of T and T when taken alone, represents a member selected from an alkoxy radical and an alkylthio radical, and T and T when taken together, represent the atoms necessary to complete a cyclic radical selected from cyclic oxyacetals and cyclic thioacetals having from 5 to 6 atoms in the heterocyclic acetal ring, and (3) a l-hydrazonoalkyl radical; and

(F) R represents either a hydrogen atom, an alkyl radical, an aralkyl radical, an alkylthio radical or an arylradical such as phenyl and naphthyl, and including substituted aryl radicals.

In certain preferred embodiments of this invention, the N-substituted, cycloammonium quaternary salts are those which contain N-substituted alkyl radicals having the terminal carbon atom substituted with a hydrazono radical, an acyl radical such as a formyl radical, an acetyl radical or a benzoyl radical, and those which have a dihydroaromatic ring nucleus such as, for example, a dihydropyridinium nucleus.

Generally, the fogging agents can be incorporated in at least one layer of the photographic element in waterpermeable association with the silver halide emulsion or they can be contacted with the emulsion before or during development such as by a pre-bath or incorporating the fogging agent in the developer composition; however, the fogging agents are preferably located in at least one layer of the element and, in a highly preferred embodiment, they are located in the silver halide emulsion layer. Concentrations of from about 75 to about 1500 mg. of the subject fogging agents per mole of silver in the silver halide emulsion are useful, with from about to about 1200 mg. of said compounds or agents per mole of silver being preferred. These ratios are according to conventional practice, however, and with either particular reversal emulsions, fogging compounds of varying chemical activity, or varying processing conditions, more widely varying fogging agent concentrations can be advantageously used.

Typical useful selective fogging agents include 2-methyl-3- 3- (p-sulfophenylhydrazone propyl] benzo-- thiazolium bromide,

hydrazine dihydrochloride,

phenylhydrazine hydrochloride,

p-methyl sulfonamide ethyl phenyl hydrazine,

formyl-4-methyl phenyl hydrazide,

3-(2-formylethyl)-2-rnethylbenzothiazolium bromide,

3-(2-acetylethyl)-2-benzylbenzothiazolium bromide,

3-(2-acetylethyl)-2-benzylbenzoselenazolium bromide,

1,2-dihydro-3-methyl-4-phenylpyrido[2,1-b1benzothiazolium bromide,

4,4'-ethylene bis(1,2-dihydro-3-methylpyrido[2,1-b]

benzothiazolium bromide),

2-methyl-3 3-p-nitrophenylhydrazono propyl] naphtho- [2,1-d]thiazolium iodide,

and the like.

The silver halide emulsions of this invention can be made by any of the precipitation and ripening procedures used for making silver halide grains. Typical procedures Include single-jet procedures, double-jet procedures, procedures utilizing automatic proportional control means to maintain specified pAg and pH, procedures using ripening agents such as thiocyanates, thioethers and/or ammonia, procedures utilizing an increase in flow rates as disclosed in Wilgus, U.S. Ser. No. 11,838 filed Feb. 16, 1970, hot nucleation procedures as disclosed in Musliner, U.S. Ser. 11:12). 31,351 filed Apr. 23, 1970, now abandoned, and the The silver halide compositions made for use in the systems of this invention are preferably monodispersed, and in some embodiments are preferably large-grain emulsions made according to Wilgus, U.S. Ser. No. 11,838, now abandoned, which is incorporated herein by reference. The monodispersed emulsions are those which comprise silver halide grains having a substantially uniform diameter. Generally, in such emulsions, no more than about by weight, of the silver halide grains smaller than the mean grain size and/or no more than about 5%, by number, of the silver halide grains larger than the mean grain size vary in diameter from the mean grain diameter by more than about 40%. Preferred photographic emulsions of this invention comprise silver halide grains, at least 95%, by weight, of said grains having a diameter which is within 40%, preferably within about 30%, of the mean grain diameter. Mean grain diameter, i.e., average grain size, can be determined using conventional methods, e.g., such as projective area as shown in an article by Trivelli and Smith entitled Empirical Relations between Sensitornetric and Size-Frequency Characteristics in Photographic Emulsion Series in The Photographic Journal, vol. LXXIX, 1939, pp. 330-338. The aforementioned uniform size distribution of silver halide grains is a characteristic of the grains in monodispersed photographic silver halide emulsions. Silver halide grains having a narrow size distribution can be obtained by controlling the conditions at which the silver halide grains are prepared using a double-run procedure. In such a procedure, the silver halide grains are prepared by simultaneously running an aqueous solution of a water-soluble silver salt, for example, an alkali metal halide such as potassium bromide, into a rapidly agitated aqueous solution of a silver halide peptizer, preferably gelatin, a gelatin derivative or some other protein peptizer. The pH and the pAg employed in this type of procedure are interrelated. For example, changing one while maintaining the other constant at a given temperature can change the size frequency distribu tion of the silver halide grains which are formed. However, generally the temperature is about 30 to about 90 C., the pH is up to about 9, preferably 4 or less, and the pAg is up to about 9.8. Suitable methods for preparing photographic silver halide emulsions having the required uniform particle size are disclosed in an article entitled Ia: Properties of Photographic Emulsion Grains, by Klein and Moisar, The Journal of Photographic Science, vol. 12, 1964, pp. 242-251; an article entitled The Spectral Sensitization of Silver Bromide on Different Crystallographic Faces, by Markocki, The Journal of Photographic Science, vol. 13, 1965, pp. 85-89; an article entitled Studies on Silver Bromide Sols, Part I. The Formation and Aging of Monodispersed Silver Bromide Sols, by Ottewill and Woodbridge, The Journal of Photographic Science, vol. 13, 1965, pp. 98-103g and an article entitled Studies on Silver Bromide Sols, Part H. The Effect of Additives on the S01 Particles, by Ottewill and Woodbridge, The Journal of Photographic Science, vol. 13, 1965, pp. 104-107.

The photographic emulsions and elements described in the practice of this invention can contain various colloids alone or in combination as vehicles, binding agents and various layers. Suitable hydrophilic materials include both naturally occurring substances such as proteins, for example, gelatin, gelatin derivatives, cellulose derivatives, polysaccharides such as dextran, gum arabic and the like; and synthetic polymeric substances such as water-soluble polyvinyl compounds like poly(vinylpyrrolidone), acrylamide polymers and the like.

The described photographic emulsion layers and other layers of a photographic element employed in the practice of this invention can also contain, alone or in combination with hydrophilic, water-permeable colloids, other synthetic polymeric compounds such as dispersed vinyl compounds such as in latex form and particularly those which increase the dimensional stability of the photographic materials. Suitable synthetic polymers include those described, for example, in US. Patents 3,142,568 by Nottorf issued July 28, 1964; 3,193,386 by White issued July 6, 1965; 3,062,674 by Houck et al. issued Nov. 6, 1962; 3,220,844 by Houck et al. issued Nov. 30, 1965; 3,287,289 by Ream et al. issued Nov. 22, 1966; and 3,411,911 by Dykstra issued Nov. 19, 1968; particularly effective are those water-insoluble polymers or latex copolymers of alkyl acrylates and methacrylate, acrylic acid, sulfoalkyl acrylates or methacrylates, those which have cross-linking sites which facilitate hardening or curing, those having recurring sulfobetaine units as described in Canadian Patent 774,054 by Dykstra, and those described in US. Patent 3,488,708 by Smith issued Jan. 6, 1970.

The photographic layers and other layers of a photographic element employed and described herein can be coated on a wide variety of supports. Typical supports include cellulose nitrate film, cellulose ester film, poly (vinyl acetal) film, polystyrene film, poly(ethylene terephthalate) film, polycarbonate film and related films or resinous materials, as well as glass, paper, metal and the like. Typically, a flexible support is employed, especially a paper support, which can be partially acetylated or coated with baryta and/or an alpha-olefin polymer, particularly a polymer of an alpha-olefin containing 2 to 10 carbon atoms such as polyethylene, polypropylene, ethylenebutene copolymers and the like.

This invention may be used with elements designed for colloid transfer processes such as described in US. Patent 2,716,059 by Yutzy et al.; silver salt diffusion transfer processes such as described in US. Patents 2,352,014 by Rott, 2,543,181 by Land, 3,020,155 by Yackel et al. and.

2,861,885 by Land; color image transfer processes such as described in US. Patents 3,087,817, 3,185,567 and 2,983,606 by Rogers, 3,253,915 by Weyerts et al., 3,227,- 550 by Whitmore et al., 3,227,551 by Barr et al., 3,227,- 552, by Whitmore and 3,415,644, 3,415,645 and 3,415,646 by Land, and US. Ser. Nos. 27,990 and 27,991, both filed Apr. 13, 1970 both now abandoned; and imbibition transfer processes as described in US. 'Patent 2,882,156 by Minsk.

This invention may be used with elements designed for color photography, for example, elements containing color-forming couplers such as those described in US. Pats. 2,376,679 by Frohlich et al., 2,322,027 by Jelley et al., 2,801,171 by Fierke et al., 2,698,794 by Godowsky, 3,227,554 by Barr et al. and 3,046,129 by Graham et al.; or elements to be developed in solutions containing colorforming couplers such as those described in US. Pats. 2,252,718 by Mannes et al., 2,592,243 by Carroll et al. and 2,950,970 by Schwan et al.; and in false-sensitized color materials such as those described in US. Pat. 2,763,549 by Hanson.

The invention can be further illustrated by the following examples of preferred embodiments thereof.

EXAMPLE 1 Use of negative sensitizing dye A primitive cubic-grain silver bromide emulsion having an average grain size of about 0.2 micron is prepared by adding an aqueou solution of potassium bromide and an aqueous solution of silver nitrate simultaneously to a rapidly agitated aqueous gelatin solution at a temperature of 70 C., over a period of about 35 minutes with a constant pAg of 8.9. After Washing in a conventional manner, the emulsion is coated on a film support at 108 mg. silver/ft. and 400 mg. gelatin/fif To separate portions of the coated emulsion are added the dyes listed in Table 1 at 800 mg./silver mole. The spectrally sensitized emulsions are then exposed imagewise on a Bausch and Lomb wedge spectrograph, exposed uniformly by an Ascor electronic flash filtered for a maximum wavelength of transmission at 380 nanometers and developed in an Elon-hydroquinone developer for 2 minutes. When the imagewise exposure is between second and the flash at 10 second is at a distance of at least 6 inches, a direct-positive image having excellent discrimination results. 1

TABLE 1 Relative reversal speed at 800 mg. n E dye mole of Ag =CH-C=CHC Dye structure Control.-... No dy Dye C: N in Mg./mole of N- butyl paraquat CH2CH2OHCH3 omomomsos Mg./mole of Dye A:

The coatings are then exposed on a Bausch and Lomb 75 Spectrograph at a slit width of 0.5 mm. for 0.5 second,

1 No reversal. 2 More negative than -1.5.

EXAMPLE 2 A silver bromide emulsion prepared as described in 70 Example 1 is coated on a film support at 108 mg. silver/ ft. T 0 separate portions of the coated emulsion are added Dye A and N-butyl paraquat (1,1-di-butyl 4,4 bipyridnum dibromide) at the levels described in the following table.

11 exposed uniformly with an Ascor electronic lamp and processed in an Elon-hydroquinone developer for 2 minutes. Direct-positive images having excellent discrimination are obtained.

12 added to separate portions of the emulsion and the emulsion samples are coated at 108 mg. silver/ft. and 400 mg. gelatin/ft}.

The resulting coatings are exposed on a Bausch and EXAMPLE 3 5 Lomb wedge spectrograph for 0.10 seconds at a slit width f 0.5 mm. and then developed for 6 minutes at 70 F. The reversal effect described in Examples 1 and 2 can 9 be supersensitizedby combining sensitizing dyes as illusm a developer havmg the follOWmg composition. G trated below. Elon 5 To a silver bromide emulsion prepared and coated as H 'z 'i described in Example 1 are added the sensitizing dyes as 10 g g ulfite described in the following table. After processing as Sodium drgxid described in Example 1, the following positive results 5 h are observed et y b zotnazole .02

4-(B-methanesulfonamrdoethyl)phenyl hydrazine hy- MgJit. MgJitfl of Relative speed drochloride 2,0 of Dye A supersensitizer at 655 nm. D l li id 13 4 800 10 Trisodium phosphate 75.0 800 40 Water to 1 liter. s00 Dye PH: 1 1'2.

Dye Structure E; E,

I S +.49 -1.4s

=OHC=CHC \e III N El; 0= 0 iii; MeOOHaCHr-Ii N-CHzCHzOMe \C/ ll EXAMPLE 4 The undyed coating shows no fog while the dyed coat- A silver bromide emulsion is prepared as in Example mgs l". lpcreasmg fog Wlth inclfasing y ls. Wh n 1. After washing the emulsion in a conventional manner, the Sensltlzmg y fl net l3 osltlve charge d 111811 sensitizing dyes at 200, 400 and 800 mg./mo1e silver are 7 level of fog, POSltlVe I age 18 Obtamed.

TABLE 2 Dye ml Relative F In .111 8 Dye Dye structure 8 sll er gge d awed? Control--- Bea Table 1..- ()4 A fin .06 .72 1.44

c an W 1.34 1.59 1.62

D --de ,11 1.14 1.64

E E fi y .05 .05 .05

F--".: --do-.. A); .04 1.32

G (in .05 .48

H .r d .05 .72 1. as

J 0 0 .06 I! ll .08 HzC-S C-NC-OH 16 I OCH(i'JC I HzC-IFI Me S-OS (E,,=+0.49; Ee=1.47)

K .r. S S .05 .05 .05 l /C=CH-(IJ=OHC\ I 01 E 01 r i CHaCHgCHCHa CHaOHgCHCHs A039 03H In all the above cases where the dye is either cationic or a zwitterionic (carries a net positive charge), i.e., A, C, D, F, G and H, a good reversal image is obtained in both the areas of absorption by the silver halide from 360-470 nm. and in the region of spectral sensitization by the dye. The background fog density is observed to be proportional to the level of dye coated. As the level of dye is increased from 200-800 mg./mle of silver, the minimum density in the exposed region decreases and the fog density in the unexposed areas increases, giving rise to the best direct-positive image at the highest dye levels.

Similar results are obtained when the reactive N-substituted cycloammonium quaternary salts 2-methyl-[3-(psulfophenylhydrazono propyl] benzothiazolium bromide, 3-(2 formylethyl) 2 methyl benzothiazolium bromide, and 2-methyl 3 [(3-p-nitrophenylhydrazono)propyl] naphtho[2,l-d]thiazolium iodide are substituted in the developer for the hydrazine compound.

EXAMPLE 5 Primitive silver bromide emulsions having an average grain size of 0.8 micron are prepared containing Dyes J, E and K as listed in Example 4 at 800 mg. of dye per mg. of silver. The emulsions are coated on a support, exposed and processed in a fogging developer, as described in Example 4, which additionally contains 1 g. of l-phenyl-Z-picolinium bromide per liter. The photographic elements yield good positive images upon development.

Similar results are obtained when the charge neutralizer dodecyl trimethylammonium para-toluenesulfonate is added to the fogging developer used to develop the above photographic elements.

EXAMPLE 6 A silver bromide emulsion is prepared, exposed and processed as described in Example 4. To separate portions of the emulsion a dye and a supersensitizer are The use of supersensitizer Dye G not only is observed to increase the efiiciency of spectral sensitization giving a 0.6 log E speed increase in reversal speed over Dye A coated alone, but the supersensitizing combination results in a greater fogging propensity with a lower level of the spectral-sensitizing Dye A. The supersensitizer thus enhances not only the photolytic interaction of the dye With the silver halide, but it also enhances the chemical fogging propensity of the silver halide.

Although the invention has been described in considerable detail with particular reference to certain preferred embodiments thereof, variations and modifications can be eifected within the spirit and scope of the invention.

We claim:

1. A process for producing a positive silver image comprising (1) imagewise exposing for at least 0.01 second at an intensity of at least about 1X10 watt/cm. a silver halide photographic element comprising a support having thereon at least one layer of an unfogged, primitive, silver halide emulsion which contains a methine or polymethine spectral-sensitizing dye present in a concentration above that which will lower the blue-speed sensitivity of a sulfur-and gold-surface-sensitized silver bromoiodid (6 mole percent iodide) emulsion of equivalent grain size at least 0.3 log E when developed in Kodak Developer D-l9, said dye having a cathodic halfwave potential less positive than 1.0 and an anodic halfwave potential more positive than +0.4 and silver halide grains which are substantialy free of any specific chemically induced internal or surface sensitivity, and then (2) either (a) developing in a silver halide developer in the presence of a chemical fogging agent or (b) light-flashing to fog said exposed silver halide emulsion for less than 0.05 second at an intensity at least ten times that of the imagewise exposure before development in a silver halide developer.

2. A process according to claim 1 wherein said silver halide is developed in a silver halide developer in the presence of a hydrazine fogging agent.

3. A 'process according to claim 1 wherein said silver halide is developed in a silver halide developer in the presence of a fogging agent which is a reactive N-substituted cycloammonium quaternary salt.

4. A process according to claim 1 wherein said silver halide developers are surface-image developers.

5. A process according to claim 1 wherein said silver halide developers are total-image developers which contain silver halide solvents.

6. A process according to claim 1 wherein said imagewise exposure is a low-intensity exposure of at least 0.01 second in duration and said element is given a highintensity over-all light flash of less than 0.05 second in duration before development in a silver halide developer.

7. A process according to claim 1 wherein said silver halide element is developed in a silver halide developing composition in the presence of a fogging agent and a charge neutralizer.

8. A photographic element comprising a support having thereon at least one layer; at least one of said layers comprising an unfogged silver halide emulsion containing silver halide grains which are substantially free of any specific chemically induced internal or surface sensitivity and a methine or polymethine spectral-sensitizing dye present in said silver halide emulsion in a concentration above that which will lower the blue-speed sensitivity of a sulfur-and gold-surface-sensitized silver bromoiodide (6 mole percent iodide) emulsion of equivalent grain size at least 0.3 log E when developed in Kodak Developer D-19, said dye having a cathodic halfwave potential less positive than l.0 and an anodic halfwave potential more positive than +0.4; at least one said layer containing a fogging agent in water permeable association with said silver halide emulsion.

9. A photographic element according to claim 8 wherein said fogging agent is a hydrazine compound.

10. A photographic element according to claim 8 wherein said fogging agent is a reactive N-substituted cycloammonium salt.

11. A photographic element according to claim 8 wherein the silver halide emulsion comprises silver halide grains wherein the halide is predominantly bromide.

12. A photographic element according to claim 8 wherein said sensitizing dye is a positively charged dye.

13. A photographic element according to claim 8 wherein said photographic element comprises layers thereon containing at least two sensitizing dyes.

References Cited UNITED STATES PATENTS 2,184,013 12/ 1939 Leermakers 96129 2,456,953 12/1948 Knott et al. 96-64 NORMAN G. TORCHIN, Primary Examiner W. H. LOUIE, In, Assistant Examiner U.'S. Cl. X.R. 96-101, 94 

